Blowers for removing slag and other fouling materials from the heated surfaces of large boilers and other heat exchangers such as are employed in public utility and industrial applications have generally employed steam as the blowing medium. It has been known for many years that where steam jets will not remove the fouling material, it can frequently be dislodged by means of a water jet. Until the development of the variable speed/constant progression-high energy water cleaning system disclosed in U.S. Pat. No. 3,782,336, granted Jan. 1, 1974, to John E. Nelson, it was frequently infeasible to utilize a waterjet however, because of the thermal shock induced by prior water cleaning systems. In many cases it was therefore necessary to shut down the boiler periodically, allow it to cool, and remove solidified slag with jackhammers and/or explosives. Although the system of the Nelson patent enabled slag removal by water in situations which previously prevented its use, it is of course preferable to avoid any thermally induced stresses whatever, except when steam blowing is not effective. Where fossil fuels are being burned, the rate of slag buildup and the tenacity of the slag are apt to vary, and successful removal by steam may be possible for some periods but not at all times. The object of the present invention is to provide an improved lance tube construction having separate nozzles for water and for steam and incorporating simple, reliable automatic means for closing the steam nozzle when water is fed to the lance, and for automatically opening the steam nozzle when steam is fed to the lance.
Other objects and advantages will become apparent to persons skilled in the art upon consideration of the present disclosure in its entirety.